Brookhaven AGS Experiment 949

Results (from the first 20% of the running approved by DOE-OHEP)

E949 has observed three additional K+→π+νν candidate events in the phase space region below the K+ → π+ π0 (Kπ2) peak (0808.2459). The new branching ratio, based on seven candidate events in the entire E787+E949 data sample, is BR=1.73+1.15-1.05x10-10. (8/18/2008)

The first E949
K+→π+ν ν candidate event
(The third event ever observed); the new branching ratio
remains almost twice the SM level
BR=1.47+1.30-0.89x10-10. This result comes from the
phase space region above the Kπ2 peak. (3/23/2004)

E949 results from the search for K+→π+γγ near the kinematic endpoint and for
K+→π+γ. (5/24/2005)

Although it is clear that
additional running is needed to evaluate consistency with the SM
prediction, funding for the completion of E949 is not yet available.
(The United States Department of Energy's Office of High Energy Physics
has neglected to provide the funding to complete the operations of E949
that they approved in August of 1999.)

Description of the experiment

We are seeking to measure the branching ratio
of K+ → π+ ν ν. E949 is a successor experiment to the very
successful E787
experiment. E787 was the first
experiment to observe this very rare decay. The first event was
collected during the 1995 run at the AGS. More information on E787
can be found at the web site,
or in the
following brief
description. The second event
was found in the 1998 data set of
E787. E949 has substantially upgraded the photon veto system, the
trigger, the data acquisition, and several other key detector systems,
and plans to run with the full AGS beam intensity (x5 more than was
available for the observation of the first event).